Method for making alkoxy-modified silsesquioxanes

ABSTRACT

A method is presented for making alkoxy-modified silsesquioxanes (AMS) or co-alkoxy-modified silsesquioxanes (co-AMS,) comprising the steps of (a) combining as a reaction mixture (i) water, (ii) an acid-stable solvent for the water, (iii) a solid strong cationic hydrolysis and condensation catalyst, and (iv) a trialkoxysilane compound, (b) allowing the reaction mixture to react for about 0.5 hours to about 200 hours to form the alkoxy-modified silsesquioxanes; and (c) recovering the alkoxy-modified silsesquioxanes from the reaction mixture. The use of solid strong cationic catalysts in this reaction system is advantageous because they remain as solids throughout the reaction, allowing simplified separation of the solid catalyst from the soluble AMS or co-AMS products, resulting in total or near total recovery of the AMS or co-AMS products, the products being free of, or substantially free of residual acid catalyst, as well as virtual total recovery of the catalyst for recycling. The improved AMS and co-AMS compounds, vulcanizable rubber compounds containing them, and a pneumatic tire having a component made from the vulcanized rubber compounds are also presented.

BACKGROUND OF THE INVENTION

As the present trend in tire-making technology continues toward the useof higher silica loadings in rubber compounds, there is a challenge tocontain levels of environmentally released volatile organic compounds(VOC), especially alcohol, during compounding, processing, cure andstorage of silica-reinforced rubbers.

In our U.S. patent application Ser. No. 11/387,569, filed Mar. 23, 2006,entitled “Compounding Silica-Reinforced Rubber With Low Volatile OrganicCompound (VOC) Emission,” the entire disclosure of which is herebyincorporated by reference, we described the preparation ofalkoxy-modified silsesquioxane (AMS) compounds and co-alkoxy-modifiedsilsesquioxane (co-AMS) compounds that generate less alcohol thanconventional alkoxysilane-containing silica-coupling and/or silicadispersing agents used in rubber compounding. In addition to improvedenvironmental conditions in the plant, the decreased amount of alcoholproduced when using the AMS and co-AMS compounds results in vulcanizedrubber compounds having one or more improved properties such as, but notlimited to, enhanced rubber reinforcement, increased polymer-fillerinteraction and lower compound viscosity, providing for tires havingimproved wet and snow traction, lower rolling resistance, increasedrebound and decreased hysteresis.

In the aforementioned patent application, we described AMS and co-AMScompounds that can be made by subjecting one or more trialkoxysilanes ortrichlorosilanes to hydrolysis and condensation in an aqueous alcoholsolution in the presence of a hydrolysis and condensation catalyst suchas, but not limited to, a strong acid (e.g., hydrochloric acid, sulfuricacid, phosphoric acid, and the like), a strong base (e.g., sodiumhydroxide, potassium hydroxide, lithium hydroxide, and the like), astrong organic acid, and a strong organic base (e.g. hindered aminebases, guanidines, and the like). The AMS or co-AMS product can beremoved from the reaction mixture, such as by phase separation,filtration, and/or extraction with water and an organic solvent, and thelike. The product can then be dried to remove substantially any organicsolvent and water remaining in the reaction mixture.

When a strong liquid acid, base, organic acid or organic base is used asthe hydrolysis and condensation catalyst, carryover of the liquidcatalyst in the precipitated AMS or co-AMS product can require specialtreatment for its removal. Therefore, an alternative method for makingAMS or co-AMS products is here presented.

SUMMARY OF THE INVENTION

It has been unexpectedly discovered that inorganic solid acidsincluding, but not limited to, solid strong cationic resins such asthose used for cationic ion exchange chromatography in, for example, thepetroleum industry, can be employed as the hydrolysis and condensationcatalyst in the production of the AMS and/or co-AMS compounds when astrong acid is desired as the catalyst. The use of such solid strongcationic catalysts in this reaction system is advantageous because theyremain as solids throughout the reaction, allowing simplified separationof the solid catalyst from the soluble AMS or co-AMS products, resultingin total or near total recovery of the AMS or co-AMS products withoutacid carryover, as well as virtual total recovery of the catalyst forrecycling.

In particular, a method is presented for making alkoxy-modifiedsilsesquioxanes or co-alkoxy-modified silsesquioxanes, comprising thesteps of (a) combining as a reaction mixture (i) water, (ii) anacid-stable solvent for the water, (iii) a solid strong cationichydrolysis and condensation catalyst, and (iv) a trialkoxysilanecompound, (b) allowing the reaction mixture to react for about 0.5 hoursto about 200 hours to form the alkoxy-modified silsesquioxanes; and (c)recovering the alkoxy-modified silsesquioxanes from the reactionmixture. The resulting products consist essentially of a mixture ofalkoxy-modified silsesquioxanes having an open structure with a reactivealkoxysilyl group, and are essentially free of closed caged polyhedralorganosilsesquioxanes. Further, the resulting products are free of, orsubstantially free of, residual acid catalyst. The method can furthercomprise the step of recovering the solid strong cationic catalyst fromthe reaction mixture for recycling the catalyst.

The invention also encompasses an improved alkoxy-modifiedsilsesquioxane obtained by a method according to the invention, whereinthe alkoxy-modified silsesquioxane is free of, or substantially free, ofresidual acid catalyst; and a vulcanizable rubber compound comprising anelastomer, a reinforcing filler comprising silica or a mixture thereofwith carbon black, a silica dispersing aid comprising an improvedalkoxy-modified silsesquioxane rubber obtained by a method according tothe invention, wherein the alkoxy-modified silsesquioxane is free of orsubstantially free of, residual acid catalyst, and a cure agent. Theinvention further encompasses a pneumatic tire including at least onecomponent comprising a vulcanized rubber made from the vulcanizablerubber compound.

DETAILED DESCRIPTION OF THE INVENTION

A method is presented for making an alkoxy-modified silsesquioxanecomprising one or more compounds selected from the group consisting ofalkoxy-modified silsesquioxanes having the formula

and mixtures, thereof, wherein w, x and y represent mole fractions, ydoes not equal zero, either w or x but not both can be zero, andw+x+y=1.00, the method comprising the steps of:

-   -   (a) combining as a reaction mixture (i) water, (ii) an        acid-stable solvent for the water, (iii) a solid strong cationic        hydrolysis and condensation catalyst, and (iv) an        R-trialkoxysilane,        -   wherein R comprises a group bonded to the silicon atom and            is independently selected from the group consisting of R¹,            R² and R³, wherein R¹, R² and R³ are the same or different            and selected from the group consisting of (i) H or an alkyl            group having one to about 20 carbon atoms, (ii) cycloalkyl            groups having 3 to about 20 carbon atoms, (iii) alkylaryl            groups having 7 to about 20 carbon atoms, and (iv) R⁵X,            wherein X is selected from the group consisting of Cl, Br,            SH, S_(a)R⁶, NR⁶ ₂, OR⁶, CO₂H, SCOR⁶, CO₂R⁶, OH, olefins,            amino groups and vinyl groups, wherein a=2 to about 8, R⁵ is            selected from the group consisting of alkylene groups having            one to about 20 carbon atoms, cycloalkylene groups having 3            to about 20 carbon atoms, and R⁴ and R⁶ are selected from            the group consisting of alkyl groups having one to about 20            carbon atoms, cycloalkyl groups having 3 to about 20 carbon            atoms, and alkylaryl groups having 7 to about 20 carbon            atoms;    -   (b) allowing the reaction mixture to react for about 0.5 hours        to about 200 hours to form the alkoxy-modified silsesquioxanes;        and    -   (c) recovering the alkoxy-modified silsesquioxanes from the        reaction mixture.

When produced according to the method, the recovered alkoxy-modifiedsilsesquioxanes consist essentially of a mixture of alkoxy-modifiedsilsesquioxanes having an open structure with a reactive alkoxysilylgroup, and are essentially free of closed caged polyhedralorganosilsesquioxanes. Further, the recovered silsesquioxanes are freeof, or substantially free of, residual acid catalyst.

In general, the AMS or co-AMS compound(s) can be made by subjecting oneor more trialkoxysilanes to hydrolysis and condensation in an aqueousalcohol solution in the presence of a solid strong cationic catalyst.The reaction is continued for a period of time sufficient forsubstantial total conversion of the trialkoxysilane(s) to the AMS orco-AMS compounds. As described below, it has been found that the rate ofconversion of the reactants to the final product can be controlled bythe concentration of the reactants (trialkoxysilane(s), acid and water),as well as the ratio of the trialkoxysilane(s) to the water. Inparticular, the greater the concentration of the reactants, the shorterthe reaction time.

In one embodiment of the method according to the invention, theacid-stable solvent for the water can be any polar protic solventincluding, but not limited to, any alcohol such as ethanol, methanol,butanol, n-propanol, isopropanol, and the like, and mixtures of these.More suitably, the alcohol is selected from ethanol, methanol, andmixtures of these. The use of alcohol allows for further additions ofwater and trialkoxysilanes to provide a continuous reaction. In thisembodiment, the step of recovering the AMS or co-AMS from the reactionmixture can comprise separating the mixture of alkoxy-modifiedsilsesquioxanes from the solid strong cationic catalyst by adding to thereaction mixture water and a nonpolar solvent for the silsesquioxanesand allowing phase separation of the water/alcohol and the nonpolarsolvent. For example, it is suitable to add water to the reactionmixture with the nonpolar solvent, prior to phase separation, to dilutethe solvent and allow any alcohol that may be soluble in the solvent toenter the water phase. Any remaining silsesquioxanes in the reactionmixture can be re-extracted with water and the nonpolar solvent.

The recovery of the mixture of alkoxy-modified silsesquioxanes from thenonpolar solvent phase can be accomplished by any known method such as,but not limited to, decantation of the nonpolar phase containing the AMSor co-AMS product, followed by drying in a warm vacuum oven, and thelike, to remove the solvent and any water that may be present. Theresulting AMS or co-AMS product is a liquid or a solid, suitably ahighly viscous liquid and, more suitably, a slightly viscous liquid,substantially free of moisture, free alcohol and residual acid catalyst.The solid strong cationic catalyst can easily be recovered from thereaction mixture as a precipitate in the water/alcohol phase, such as byfiltration and the like, providing for its reuse in subsequentreactions.

Any nonpolar solvent for AMS or co-AMS product can be used to separatethe product from the solid catalyst. Suitable nonpolar solvents include,but are not limited to, hexane, cyclohexane, benzene, toluene, and thelike, and mixtures of these.

In another embodiment of the method, a polar aprotic solvent for thewater can be used in place of the polar protic solvent. Suitable polaraprotic solvents include, but are not limited to, tetrahydrofuran (THF),1,4-dioxane, 1,3-dioxolane, acetone, acetonitrile, diethyl ether, ethylacetate, and the like, and mixtures of these. Such solvents are alsosolvents for the AMS and co-AMS products of the reaction. Therefore, itis not necessary to add a nonpolar solvent for the products to separatethe products from the solid catalyst. Although it is recognized thatacetone, ethyl acetate, and THF can very slowly react with the acidcatalyst under certain conditions, no significant reaction of this typetakes place under the conditions of time, temperature, and concentrationof the acid employed in the invention methods.

The use of the solid catalyst in this embodiment is particularlyefficient. Because of the solubility of the AMS or co-AMS products inthe polar aprotic solvent, residual alkoxysiloxane groups can beminimized by extending the reaction time to allow further hydrolysis andcondensation. In this embodiment, the method proceeds as above in steps(a) through (c). Recovery of the mixture of AMS or co-AMS products canbe accomplished by any known method such as, but not limited to,decantation of the polar aprotic phase containing the AMS or co-AMSproduct, followed by drying in a warm vacuum oven, and the like, toremove the solvent and any water that may be present. Again, theresulting product is a liquid or a solid, suitably a highly viscousliquid and, more suitably, a slightly viscous liquid, substantially freeof moisture, of free alcohol and of residual acid catalyst. The solidstrong cationic catalyst can easily be recovered from the reactionmixture as a precipitate, such as by filtration and the like, providingfor its reuse in subsequent reactions.

Suitable solid strong cationic hydrolysis and condensation catalysts foruse in making the AMS or co-AMS products are commercially available andinclude, but are not limited to, cationic ion exchange resins that havesulfonic acid groups attached to an insoluble polymeric matrix. Thesesolid resins contain a H⁺ counter ion that is a strong cation exchangerdue to its very low pKa (<1.0). As a non-limiting example, such cationicion exchange resins can be prepared by sulfonating (by treating withsulfuric acid) a polystyrene that has been crosslinked with about 1percent to about 8 percent divinylbenzene. Examples of suitablecommercially available strong cationic exchange resins include, but arenot limited to, the H⁺ ionic form of Amberlite IR-120, Amberlyst A-15,Purolite C-100, and any of the Dowex® 50WX series resins. Such resinsare typically gel beads having particle sizes of about 400 mesh to about50 mesh. The particle size is not crucial in the methods of theinvention. Other types of solid supports for the strong cationic ionshave been described, such as, but not limited to, polymer strips,polymer membranes, and the like. Such alternative forms are within thescope of the invention, as claimed. Suitably, the solid strong cationiccatalysts are in a physical form that, after the AMS or co-AMS productsare extracted, will precipitate (or sink) to the bottom of the reactionchamber for simple separation from the reaction mixture, such as byfiltration or the like.

It has been observed that new resins frequently contain free sulfuricacid that is present from the sulfonation procedure. This free acid cancause a high viscosity of the AMS or co-AMS product formed in thehydrolysis and condensation reaction. Therefore, it is desirable toremove this free acid by washing with water and a solvent for the water.By using a solvent for the water in addition to the wash water, it hasbeen found that there is less residual water retained by the resin.

As described further below, it has been observed that a catalytic amountof the solid strong cationic catalyst used in the reaction can be aslittle as about 1% to about 50%, suitably about 5% to about 40%, of themolar amount of the acid and the trialkoxysilane used in thepreparation.

The temperature at which the reaction takes place is not critical exceptthat it be less than the boiling point of the solvent. For example,almost identical compositions of AMS or co-AMS product can be obtainedfrom ambient temperature (about 25° C.) to about 60° C. to about 100° C.The expected rate enhancement of the reaction can be attained as thetemperature increases. The AMS or co-AMS product can be observed as acloudy residue that, if desired, can be progressively removed from thereaction mixture over a period of time until there is substantiallytotal conversion of the reactants to the AMS or co-AMS product.Moreover, during the reaction, additional amounts of the trialkoxysilanereactants can be added, with water, to continuously yield product.

If a polar protic solvent for the water, such as alcohol, is used, theformation of the AMS or co-AMS can initially be observed as a cloudysolution which phase separates with increasing time. If a polar aproticsolvent, such as tetrahydrofuran (THE) is used, the AMS or co-AMS in thesolvent is essentially clear. The phase containing the products, ifdesired, can be steadily removed from the reaction mixture over a periodof time until there is substantially total conversion to the AMS orco-AMS products. Moreover, during the reaction, additional amounts ofthe trialkoxysilane reactants can be added, with water, to continuouslyyield product.

The period of time for total conversion of the reactants to the AMS orco-AMS product depends on the original concentration of the reactants,the solubility of the AMS or co-AMS in the solvent and the optionaladdition of reactants and/or applied heat during the process. However,if no additional reactants are used, the time can range from about 0.5hours to about 200 hours, often about 0.75 hours to about 120 hours, orabout one hour to about 72 hours. The time for total conversion isdefined as the time elapsed until no further product can be removed byphase separation and no further product can be extracted from thereaction mixture by water and organic solvent, as described above.

Exemplary alkyltrialkoxysilane reactants in making the AMS products caninclude, but are not limited to, octyltriethoxysilane,octyltrimethoxysilane, cyclohexyltriethoxysilane,isobutyltriethoxysilane, ethyltrimethoxysilane,cyclohexyltributoxysilane, methyltriethoxysilane, propyltriethoxysilane,hexyltriethoxysilane, heptyltriethoxysilane, nonyltriethoxysilane,decyltriethoxysilane, 3-chloropropyltriethoxysilane,3-chloropropyltrimethoxysilane, n-dodecyltrialkoxysilane,octadecyltriethoxysilane, methyltrimethoxysilane,propyltrimethoxysilane, hexyltrimethoxysilane, heptyltrimethoxysilane,nonyltrimethoxysilane, octadecyltrimethoxysilane,2-ethylhexyltriethoxysilane, and the like, and mixtures thereof.

Co-AMS compounds can be obtained by co-reacting any number oftrialkoxysilanes such as, but not limited to, alkyltriethoxysilaneand/or alkyltrimethoxysilanes, by hydrolysis and condensation with oneor more other trialkoxysilanes that can provide one or more functionalgroups (R⁵X, as defined above) on the AMS compound. As a non-limitingexample, for use in rubber compounds, it may be desirable to produce aco-AMS compound containing a sulfur atom that can bind to an elastomer.Therefore, a suitable co-AMS compound can be manufactured by theco-hydrolysis and co-condensation of an alkyltrialkoxysilane with, forexample, a mercaptoalkyltrialkoxysilane to introduce a mercaptoalkylfunctionality, or with a blocked mercaptoalkyltrialkoxysilane tointroduce a blocked mercaptoalkyl functionality. Examples of suitablesulfur-containing trialkoxysilanes include, but are not limited tomercapto-alkyltrialkoxysilanes, blocked mercaptoalkyltrialkoxysilanes,3-thioacylpropyltrialkoxy-silane, 3-thiooctanoylpropyltrialkoxysilane, atrialkoxysilane containing a chain of about 2 to about 8 sulfur atoms,and mixtures of these.

In this description the use of the term “blockedmercaptoalkyltrialkoxysilane” is defined as a mercaptosilane silicacoupling agent that comprises a blocking moiety that blocks the mercaptopart of the molecule (i.e. the mercapto hydrogen atom is replaced byanother group, hereafter referred to as “blocking group”) while notaffecting the silica-reactive mercaptosilane moiety. Suitable blockedmercaptosilanes can include, but are not limited to, those described inU.S. Pat. Nos. 6,127,468; 6,204,339; 6,528,673; 6,635,700; 6,649,684;6,683,135; the disclosures of which are hereby incorporated by referencewith respect to the examples described. For purposes of this disclosure,the silica-reactive “mercaptosilane moiety” is defined as the molecularweight equivalent to the molecular weight of3-mercaptopropyltriethoxysilane. A deblocking agent can be added duringor after rubber compounding (e.g., later in the manufacturing process,such as during cure), after the silica-silane reaction has occurred, toallow the sulfur atom of the mercaptosilane to bond rapidly with therubber. The deblocking agent can be added at any time during thecompounding process as a single component during any mixing stage inwhich deblocking is desired. Examples of deblocking agents are wellknown to those skilled in the art.

The AMS or co-AMS products resulting from the catalyzed hydrolysis andcondensation reaction can be observed as a multitude of peaks whenmeasured, for example, by high pressure liquid chromatography (HPLC),²⁹Si nuclear magnetic resonance (NMR), and the like. The oligomerscomprise a mixture of linear, branched and/or isomeric placements of thealkoxy modification. The collection of products is referred to asalkoxy-modified silsesquioxanes and/or co-alkoxy-modifiedsilsesquioxanes. For example, these alkoxy-modified silsesquioxanes caninclude, but are not limited to, octyl alkoxy-modified silsesquioxanes,phenyl alkoxy-modified silsesquioxanes, 3-mercaptopropyl alkoxy-modifiedsilsesquioxanes, 3-thioacylpropyl alkoxy-modified silsesquioxanes, andthe like, and mixtures of any of these. Thus, the alkoxy-modifiedsilsesquioxane(s) can comprise alkylalkoxy-modified silsesquioxanes,alkyl-co-mercapto alkoxy-modified silsesquioxanes, and the like, withoutlimitation.

As non-limiting examples of trialkoxysilanes that can be used in themethods of the present invention, the formula weights of the originalsilane and the perfect silsesquioxane that would be expected to formfrom the total hydrolysis reaction are illustrated in Table 1.

TABLE 1 R—SiX₃ R—SiO_(3/2) R-Silane Si—X₃ (g/mol) (g/mol) octyltriethoxy 276.5 165.31 3-mercaptopropyl trimethoxy 196.3 127.233-thiooctanoylpropyl triethoxy^(a) 364.6 253.44 phenyl triethoxy 198.3129.17 ^(a)NXT ™ (a blocked mercaptan from Crompton, Greenwich CT)These values can be used along with the mole fractions of the silanescharged to determine the approximate theoretical yield for a desired AMSor co-AMS, when using the solid strong cationic catalyst in thehydrolysis and condensation reaction.

Table 2 illustrates a non-limiting example of kinetic runs includingmolar ratios of the various ingredients that can be used to produce theAMS or co-AMS products.

TABLE 2 OTES HCl Water Run # Solvent mol/L mol protons/L mol/L A EtOH0.79 0.77 13.62 B EtOH 0.40 0.40 13.99 C EtOH 0.40 0.40 6.41 D MeOH 0.400.40 6.39 E EtOH 0.40 0.80 3.72 F EtOH 0.80 0.40 7.00

For example, runs A-D use essentially equivalent molar ratios of OTESand acid; whereas run E uses a 2% molar amount of acid and run F uses a0.5× molar amount of acid. Compared with runs A and B, runs C and D useabout one-half the molar amount of water; run E uses about one-quarterthe molar amount of water with a 2× molar amount of acid; and run F usesabout one-half the molar amount of water, but the molar amount of OTESis doubled. It was observed that there was a steady increase in theamount of AMS formed in moles/L as the concentrations of the OTES, HCland water increased (run A, data not shown). Further, the rate ofreaction for the intermediate and high level of water (runs B, C and D)was about the same at a mole ratio of 0.40 mol/L OTES. Exchanging theethanol with methanol showed about a two fold increase in the initialrate of product formation. The reduction of water to 3.7 mol/L (run E),even with a doubling of the HCl reduced the rate by about one-half,compared with run D (data not shown).

Extrapolating from these preliminary runs employing HCl as the strongacid, it can be seen that a molar catalytic amount of the protonspresent in the solid strong cationic catalyst used in the reactionsaccording to the methods of the present invention suitably can be aslittle as about 1% to about 50% and, more suitably, about 5% to about40% of the molar amount of the trialkoxysilane used in the preparation.Within the limits of practicality, there is virtually no lower or upperlimitation on the molar concentrations of the reactants.

A feature of each of the AMS or co-AMS products produced is the presenceof a reactive alkoxysilyl group “y” attached to one or morealkoxy-modified silsesquioxane “w” and/or “x” groups. In an AMScompound, either w or x but not both can be zero. In a co-AMS, w and xare not zero. The mole fraction of the one or more w or x groups iscalculated as the mole fraction of w or x divided by the sum of the molefractions w+x. Suitably, ratios of the w mole fraction (or the ratio ofthe x mole fraction) to the sum of the w+x fraction can range from about0.01 to about 0.5. The mole fractions of w, x and y also can be measuredthrough the mole factions of R¹, R², and R³ if the relative abundance ofthose groups can be measured. The sum of the mole fractions w, x and yis always equal to one, and y is not zero.

The individual weight fractions of w, x and y can be calculated from themole fraction of each times their respective formula weight (FW) dividedby the sum of the individual w, x and y weight fractions. For example,the weight percent of x (W %(x)) is calculated as

${W\%(x)} = {\frac{x\left( {FW}_{x} \right)}{{x\left( {FW}_{x} \right)} + {w\left( {FW}_{w} \right)} + {y\left( {FW}_{y} \right)}} \times 100}$The weight percent of alcohol (HOR⁴) can be calculated by the formula

${W\%\left( {HOR}^{4} \right)} = {\frac{3\left( {FW}_{{HOR}^{4}} \right)}{{x\left( {FW}_{x} \right)} + {w\left( {FW}_{w} \right)} + {y\left( {FW}_{y} \right)}} \times 100}$

The alkoxy-modified silsesquioxanes made using these methods consistessentially of “open” structures having the reactive alkoxysilyl groupand are essentially free of pure closed caged polyhedralorganosilsesquioxanes (POSS) structures that are known for use asnanoparticle fillers in various compounds. For example, a nuclearmagnetic resonance (NMR) analysis of the ²⁹Si content of an exemplaryoligomer mixture, as illustrated in the aforementioned patentapplication incorporated by reference, shows a broad range (in parts permillion, ppm) from about −47 ppm to about −71 ppm. In comparison, NMRanalysis of the ²⁹Si content of a pure closed caged POSS structure showsa definitive peak at about −68 ppm. Without being bound by theory, it isbelieved that the method of preparation of the AMS and co-AMS products,as described above and as described in the aforementioned patentapplication, precludes or minimizes the formation of pure POSSstructures because of the myriad of different geometric attachments thatthe rapid condensation of a trialkoxysilane generates. NMR spectraranges for the amount of ¹H and/or ¹³C in the products can also bedetermined, but these spectra will differ, depending on the various Rgroups attached to the structures, and are not illustrated here.

Another important feature of each of the AMS or co-AMS products producedis that the reactive alkoxysilyl group is present at such a low levelthat only a small amount of alcohol can be liberated by hydrolysis ofthe product. That is, the y alkoxysilyl group generates only about 0.05%to about 10% by weight alcohol when the product is treated bysubstantially total acid hydrolysis. Suitably, the amount of generatedalcohol is about 0.5% to about 8% by weight and, more suitably, theamount of generated alcohol is about 1% to about 6% by weight.

The amount of residual reactive alkoxysilyl groups in each of the finalAMS or co-AMS products can be measured by the amount of alcoholrecoverable from the product, according to the method published inRubber Chemistry & Technology 75, 215 (2001). Briefly, a sample of theproduct is treated by total acid hydrolysis using a siloxane hydrolysisreagent (0.2 N toluenesulfonic acid/0.24 N water/15% n-butanol/85%toluene). This reagent quantitatively reacts with residual ethoxysilane(EtOSi) or methoxysilane (MeOSi), freeing a substantially total amountof ethanol or methanol that is then measured by a headspace/gaschromatographic technique, and expressed as the percentage by weight inthe sample.

Therefore, the AMS or co-AMS product(s) produced are very suitable foruse in rubber compositions in which silica is employed as a reinforcingfiller. In particular, the reactive alkoxysilane group(s) attached tothe AMS or co-AIMS products can participate in the alkoxysilane-silicareaction and can improve silica dispersion in the rubber. Therefore, theAMS or co-AMS product(s), including those made by a method of accordingto the invention, can be used to form a vulcanizable rubber compoundcomprising (a) an elastomer; (b) a reinforcing filler comprising silicaor a mixture thereof with carbon black; (c) a silica dispersing aidcomprising an alkoxy-modified silsesquioxane obtained by the methodaccording to the invention, wherein the alkoxy-modified silsesquioxaneis substantially free of residual acid catalyst; and (d) a cure agent.The disclosure of the aforementioned patent application regarding otheradditives that can be included in the vulcanizable rubber compound, ishereby incorporated by reference.

As discussed above, the alkoxysilane-silica reaction produces alcohol asa by-product when alkyltrialkoxysilanes and/or alkoxysilane-terminatedpolymer groups are used for silica dispersion in rubber compounds.Usually, the trialkoxysilane employed is a triethoxysilane or atrimethoxysilane, and the generated alcohol is ethanol or methanol,respectively. Because these alcohol emissions add to the VOC emissionsgenerated from processing of the other rubber tire components, theamount of reinforcing silica and concomitant amount of trialkoxysilaneemployed is governed and limited by government environmentalregulations.

The limited amount of alcohol that is available in the AMS or co-AMSproduct(s) make these compounds very useful in rubber compounds becausethey have the potential to significantly reduce the level of potentialVOCs emitted as alcohol during compounding and further processing.Moreover, the limited amount of available unreacted alkoxysilane groupsduring and after mixing, severely limit the degree of blistering in thevulcanized rubber compounds and tires made from them. The use of theproducts made according to the method of the invention also allow asignificant increase in the amount of silica used for reinforcement.

The use of the AMS and/or co-AMS products, including the improvedproducts made by a method according to the invention, in rubbercompounds not only minimizes alcohol emissions during compounding andfurther processing of the rubber, but these products also perform wellas silica dispersing agents, giving improved physical properties to thestocks containing the compounds.

The vulcanized rubber compounds containing the improved AMS and/orco-AMS compounds made by a method according to the present invention canbe utilized to form products such as power belts, and treadstocks forpneumatic tires. The composition can also be used to form otherelastomeric tire components such as subtreads, sidewalls, body plyskims, bead fillers, apex, chafer, sidewall insert, wirecoat, innerliner, and the like, without limitation.

EXAMPLES

The following examples illustrate methods of preparation ofrepresentative alkoxy-modified silsesquioxanes employing a solid strongcationic resin as the hydrolysis and condensation catalyst. However, theexamples are not intended to be limiting, as other alkoxy-modifiedsilsesquioxanes, alone or in combination, can be prepared according tothe described methods. Moreover, the methods are exemplary only andother methods for preparing the alkoxy-modified silsesquioxanesemploying other solid strong cationic catalysts can be determined bythose skilled in the art without departing from the scope of theinvention herein disclosed and claimed.

Example 1 Preparation of n-Octyl Alkoxy-Modified Silsesquioxane(Octyl-AMS) Using Dowex 50WX2-200 Resin

To a 500 mL Erlenmeyer flask was added 9.23 grams (44.3 mmol of H⁺) ofdry Dowex 50WX2-200 (a strong cationic polystyrene resin crosslinkedwith 2% divinylbenzene and having sulfonic acid as the functional group,200 mesh particles), 238 mL of absolute ethanol and 27.95 grams (1.613mol) of distilled water. When the resin was uniformly dispersed, 41.36grams (150 mmol) of octyltriethoxysilane (OTES) was added. The molarratio of the silane to the H⁺ of the resin was about 30:1. Afterstirring for 17 hours, the AMS produced coated the resin as a lowerphase. The addition of 260 mL of cyclohexane and 260 mL of water gavethe AMS in the upper phase and the resin as a precipitate in the loweraqueous phase. Recovery of the resin by filtration and drying gave 6.91grams (75% of the original amount). The AMS was recovered as a highviscosity material by evaporation of the solvent to give 24.56 grams(98% of the theoretical yield, TY).

Example 2 Preparation of Octyl-AMS Using Recovered Dowex 50WX2-200 Resin

The procedure according to Example 1 was repeated, except that 6.91grams (33.2 mmol of H⁺) of recovered Dowex-50WX2-200 (from Example 1)was used in 160 mL of absolute ethanol, 21.14 grams (1.22 mol) of waterand 28.24 grams (102 mmol) of OTES. The resin in the initial reactionmixture compressed within 3 hours to less than 50% of the originaldispersed volume as the AMS formation coated the particles. Afterstirring for 24 hours, cyclohexane and water was added to isolate 17.46grams (103.4% TY) of a less viscous AMS.

Example 3 Preparation of Octyl-AMS Using Dowex 50WX2-200 Resin that wasPreviously Washed to Remove Excess Free Sulfonic Acid

The Dowex resin was twice washed with THF and water to remove the freesulfuric acid that is present in new resin. This free acid was thoughtto be the cause of the high viscosity AMS that was produced in thepreparations according to Examples 1 and 2. Thus, 15.39 grams of theDowex resin (containing 73.9 mmol of sulfonic acid, as measured bythermoanalysis) was dispersed in 150 mL of THF containing 15 mL ofwater. The mixture was stirred, decanted and washed a second time withthe THF and water. The mixture was then rinsed once more with THF. Theamount of sulfonic acid and water remaining in the catalyst slurry wasmeasured and subsequent charges of water and THF in the reaction mixtureto produce AMS were adjusted accordingly.

The reaction mixture was run according to Example 1, with the washedDowex resin, 182 mL of THF, 24.65 grams (1.77 mol) of water and 41.2grams (149 mmol) of OTES. The mixture was stirred for 24 hours andfiltered to recover the resin (12.07 grams). Evaporation of the THFyielded 24.67 grams of a desired slightly viscous AMS.

Example 4 Determination of Latent Ethanol in the AMS Produced in Example3

Prior to separating the AMS from the THF solution in Example 3, a sampleof the solution was analyzed for ethanol by head space gaschromatography. The average of 8.30% ethanol measured within one hour ofreaction time compared favorably to the 9.03% theoretical amount ofethanol that a complete reaction would produce (92% of the TY of ethanolwas obtained). Analysis of the AMS product obtained after 24 hours ofreaction time showed 0.238% latent ethanol.

While the invention has been described herein with reference to thepreferred embodiments, it is to be understood that it is not intended tolimit the invention to the specific forms disclosed. On the contrary, itis intended that the invention cover all modifications and alternativeforms falling within the scope of the appended claims.

1. A method for making an alkoxy-modified silsesquioxane comprising oneor more compounds selected from the group consisting of alkoxy-modifiedsilsesquioxanes having the formula

and mixtures, thereof, wherein w, x and y represent mole fractions, ydoes not equal zero, either w or x but not both can be zero, andw+x+y=1.00, the method comprising the steps of: (a) combining as areaction mixture: (i) water, (ii) an acid-stable solvent for the water,(iii) a solid strong cationic hydrolysis and condensation catalyst, and(iv) an R— trialkoxysilane, wherein R comprises a group bonded to thesilicon atom and is independently selected from the group consisting ofR¹, R² and R³, wherein R¹, R² and R³ are the same or different andselected from the group consisting of (i) H or an alkyl group having oneto about 20 carbon atoms, (ii) cycloalkyl groups having 3 to about 20carbon atoms, (iii) alkylaryl groups having 7 to about 20 carbon atoms,and (iv) R⁵X, wherein X is selected from the group consisting of Cl, Br,SH, S_(a)R⁶, NR⁶ ₂, OR⁶, CO₂H, SCOR6, CO₂R⁶, OH, olefins, amino groupsand vinyl groups, wherein a=2 to about 8, R⁵ is selected from the groupconsisting of alkylene groups having one to about 20 carbon atoms,cycloalkylene groups having 3 to about 20 carbon atoms, and R⁴ and R⁶are selected from the group consisting of alkyl groups having one toabout 20 carbon atoms, cycloalkyl groups having 3 to about 20 carbonatoms, and alkylaryl groups having 7 to about 20 carbon atoms; (b)allowing the reaction mixture to react for about 0.5 hours to about 200hours to form the alkoxy-modified silsesquioxanes; and (c) recoveringthe alkoxy-modified silsesquioxanes from the reaction mixture, whereinthe alkoxy-modified silsesquioxanes consist essentially of a mixture ofalkoxy-modified silsesquioxanes having an open structure with a reactivealkoxysilyl group, and are essentially free of closed caged polyhedralorganosilsesquioxanes, and wherein the mixture of alkoxy-modifiedsilsesquioxanes liberates about 0.05% to about 10% by weight alcoholwhen treated by substantially total acid hydrolysis.
 2. The method ofclaim 1, wherein the alkoxy-modified silsesquioxanes are substantiallyfree of residual acid catalyst.
 3. The method of claim 1, wherein theacid-stable solvent for the water comprises a polar protic solvent. 4.The method of claim 3, wherein the polar protic solvent comprises analcohol.
 5. The method of claim 4, wherein the alcohol is selected fromthe group consisting of absolute ethanol, absolute methanol, andmixtures thereof.
 6. The method of claim 1, wherein the recovering step(c) further comprises the substeps: (1) separating the mixture ofalkoxy-modified silsesquioxanes from the solid strong cationic catalystby adding to the reaction mixture water and a nonpolar solvent for thesilsesquioxanes; (2) allowing phase separation of the water/alcohol andthe nonpolar solvent; and (3) recovering the mixture of alkoxy-modifiedsilsesquioxanes from the nonpolar solvent phase.
 7. The method of claim6, wherein the nonpolar solvent is selected from the group consisting ofhexane, cyclohexane, benzene, toluene, and mixtures thereof.
 8. Themethod of claim 1, wherein the recovering step (c) further comprises thesubstep (4): recovering the solid strong cationic catalyst from thewater/alcohol phase.
 9. The method of claim 1, wherein the acid-stablesolvent for the water comprises a polar aprotic solvent.
 10. The methodof claim 9, wherein the polar aprotic solvent comprises a hydrocarbonsolvent for the mixture of alkoxy-modified silsesquioxanes.
 11. Themethod of claim 9, wherein the polar aprotic solvent is selected fromthe group consisting of tetrahydrofuran, 1,4-dioxane, 1,3-dioxolane,acetone, acetonitrile, diethyl ether, ethyl acetate, and mixturesthereof.
 12. The method of claim 9, wherein the recovering step (c)further comprises the substeps (5) of allowing phase separation of thepolar aprotic solvent phase and the solid strong cationic catalyst, and(6) recovering the mixture of alkoxy-modified silsesquioxanes from thepolar aprotic solvent phase.
 13. The method of claim 12, wherein therecovering step (c) further comprises the substep (7) of recovering thesolid strong cationic catalyst from the phase separation step (5). 14.The method of claim 1, wherein the hydrolysis and condensation catalystcomprises a solid strong cationic crosslinked resin.
 15. The method ofclaim 1, wherein step (a) comprises the substep of washing the strongcationic crosslinked resin to remove excess cations prior to addition ofthe catalyst to the reaction mixture.
 16. The method of claim 1, whereinat least one of the trialkoxysilanes in the reaction mixture comprises agroup that can bind to an elastomer.
 17. The method of claim 16, whereinat least one of the trialkoxysilanes in the reaction mixture is selectedfrom the group consisting of a mercaptoalkyltrialkoxysilane, a blockedmercaptoalkyltrialkoxysilane, a 3-thioacylpropyltrialkoxysilane, a3-thiooctanoylpropyltrialkoxysilane, a trialkoxysilane containing achain of about 2 to about 8 sulfur atoms, and mixtures thereof.
 18. Themethod of claim 1, wherein at least one of the trialkoxysilanes in thereaction mixture comprises an alkyltrialkoxysilane.